Android: Use setTag and getTag of View

Android: Use setTag and getTag of View

1. Used to differentiate many similar views

For example:

 

button1.setOnClickListener(new OnClickListener ... );button2.setOnClickListener(new OnClickListener ... );

They may execute similar logic, but you must set two independent OnClick events for the two buttons respectively,

 

 

public void onClick(View v) {    doAction(1); // 1 for button1, 2 for button2, etc.}

This is because onClick has only one View parameter. We can do this using setTag and getTag:

 

 

button1.setTag(1);button2.setTag(2);

We can set the two buttons to the same OnClickListener, for example:

 

 

listener = new OnClickListener() {    @Override    public void onClick(View v) {        doAction(v.getTag());    }};

In this way, it can be distinguished by getTag.

 

 

2. Used for reuse of ListView

When writing a custom adapter, we usually use it, for example:

 

static class ViewHolder {    TextView tvPost;    TextView tvDate;    ImageView thumb;}public View getView(int position, View convertView, ViewGroup parent) {    if (convertView == null) {        LayoutInflater inflater = myContext.getLayoutInflater();        convertView = inflater.inflate(R.layout.postitem, null);        ViewHolder vh = new ViewHolder();        vh.tvPost = (TextView)convertView.findViewById(R.id.postTitleLabel);        vh.tvDate = (TextView)convertView.findViewById(R.id.postDateLabel);        vh.thumb = (ImageView)convertView.findViewById(R.id.postThumb);        convertView.setTag(vh);    }            ....................}

3. Note:

 

In addition to the above situations, we try not to use them directly. The reason is:

1. code readability: it will cause troubles to other programmers.

2. Because setTag and getTag are set to an Object, a class conversion exception may occur.

However, there is a better method after android4.0: setTag (int key, Object tag) can be similar Key-Value Pair Access.